Figure 5: Stimulation above the primary motor cortex threshold causes current spread and loss of the specificity of stimulation. Panel A shows triggered mMEPs in the orbicularis oris channel triggered in two occasions: first time in sets 154 through 162 (bottom circle) and second time in sets 170 through 175 (top circle). However, panels B and C shows higher amplitude mMEPs also triggered in the brachioradialis-triceps and hand channels respectively, during sets 154-162. In these trials, the stimulation was done at current intensity (i.e. 7 mA) higher than the mapping threshold. Thus, the activity seen in orbicularis oris channel in sets 154-162 is most likely due to a spread of the current from the primary motor hand region. However, once the stimulus amplitude was decreased at 4 mA, stimulation of the face primary motor region, caused isolated mMEPs in the orbicularis oris channel (sets 170 through 175 in panel A) but not in the brachioradialis-triceps or hand channels ( see same sets in panels B and C respectively). Of note, the facial mMEPs in sets 170-175 have higher amplitude, more complex morphology and shorter latencies than the facial mMEPs triggered in sets 154 through 162, supporting the conclusion that in sets 170-175 direct (rather than indirect) stimulation of the face region occurred. Panel D in the background offers a chronological view of the overall mapping, with each column representing the activity in one muscle channel. INTRAOPERATIVE CLINICAL NEUROPHYSIOLOGY by Mirela Simon. Copyright 2010 by DEMOS MEDICAL PUBLISHING LLC. Reproduced with permission of DEMOS MEDICAL PUBLISHING LLC in the format Other book via Copyright Clearance Center.